When two shafts are not perfectly aligned to a common axis and must be coupled together, it is standard to use a flexible coupling that accommodates the misalignment, whether that be a lateral offset of one shaft axis to the other or a condition where the one shaft axis intersects the other at an angle approaching 180.degree.. Such a flexible coupling can comprise at its simplest a flexible sleeve having one end fitted to one of the shafts and an opposite end to the other shaft.
Normally as described in German patent document 2,042,260, German utility model 9,308,521, and French patent document 839,967 the two shaft ends are fitted with respective fittings whose outer surfaces are normally formed with radially outwardly directed teeth. The sleeve is split so it can be fitted over the end fittings and is internally formed with elongated teeth or ridges that fit with the teeth of the fittings, although a glue joint is also occasionally used. Normally a steel ring is fitted around the sleeve, with bumps on the ring fitting into recesses on the sleeve to maintain its position.
Installing such a coupling can be fairly difficult. Once installed it is possible for moisture and/or particles to get into the coupling to damage it. Furthermore once it is in place it is impossible to adjust it, in particular to compensate for material shrinkage or wear of the parts.